Reorganize tests to always use runtests.jl files

[fingolfin]

... to group things together. Also merge test/Experimental content into the experimental directory.

This should be mostly orthogonal to PR #2810 by @benlorenz

[benlorenz]

thanks, looks good!

[lgoettgens]

For the parallelization, it would make sense to not include experimental/runtests.jl as the last item, as that file contains a lot of tests that in total need a long time. And parallelization with pmap gets more efficient if the larger tasks are at the front and the smaller ones in the end of the list.

[fingolfin]

Sure, I can move it further up again.

That said, perhaps we should revise how we do this parallelization anyway: it would make more sense to parallelize all those include statements (under the assumption that they are all mutually independent, which they really should be).

For this, we could just take all the *.jl files under test which are not named runtests.jl, and then pass all of them to pmap. Then the runtests.jl files would just be for convenience (and they could all also become identical, with the same code that includes all "*.jl" files in "subdirectories of the current directory except for those named runtests.jl).

That would then also render the part of PR #2810 moot which checks for files that we accidentally did not include...

[benlorenz]

When I prepared #2810 I was considering including everything automatically as well. But I thought it would be easier / safer to just check the includes first.
Luckily there weren't that many missing includes. Automatically including all jl files in the test folders would be fine with me as well.

[lgoettgens]

If we are using Test in basically every testfile, we do not check that it is already loaded in

Oscar.jl/src/utils/tests.jl

Line 23 in 81b983d

@req isdefined(Base.Main, :Test) "You need to do \"using Test\""

[fingolfin]

But we currently don't do it in ever testfile, just in the runtests.jl files...